Precursor conditions or subclinical markers provide an opportunity to understand the early determinants of atherosclerosis. Traditional vascular risk factors predict less than a half of variance in carotid plaque and a half of individuals experience plaque progression despite treatment of traditional vascular risk factors according to current guidelines. Individuals with progression of subclinical atherosclerosis have twice the risk of stroke, myocardial infarction or death over 5 years, compared to those with stable plaque or regression. Atherosclerosis is a complex condition with a substantial genetic contribution. Specific genetic polymorphisms involved in regulation of subclinical carotid atherosclerosis and their extreme unexplained phenotypes are not known. A search for new alleles that either accelerate or protect from atherosclerosis, using extreme unexplained phenotypes of subclinical atherosclerosis will help identifying novel factors which may ultimately lead to innovative therapeutic targets for atherosclerosis and reduce risk of stroke, myocardial infarction and other consequences of atherosclerosis. The specific primary aims of the proposed research are to: (1) identify individuals with unexplained subclinical atherosclerosis (USAth) and unexplained protection against atherosclerosis (UPAth) by generating standardized residual scores in the multivariable regression model from traditional vascular risk factors and carotid artery plaque area burden, a subclinical carotid artery phenotype collected among 1,200 Caribbean Hispanic stroke-free individuals; (2) identify alleles that are associated with USAth and UPAth by performing a genome wide association study; (3) validate these findings in an independent sample of a family-based cohort and in the SHARe Project, and (4) perform follow-up studies of the top 2 most significant SNPs/CNVs identified in both samples to identify the underlying causative variation. The strengths of this proposal include the wealth of baseline data (including carotid ultrasound imaging) that has already been collected as a part of the population-based Northern Manhattan study, the evaluation of innovative risk factors, DNA repository available, carotid imaging performed according to the standardized scanning protocols, a capability of sophisticated ultrasound imaging analyses, genotyping and genetic analyses, and dual PI responsibility to assure a completion of the high quality phenotyping (Dr. T. Rundek, neurology) and genotyping (Dr. S. Blanton, genomics). New quantitative traits developed in this study, unexplained subclinical atherosclerosis and unexplained protection against subclinical atherosclerosis, will make possible to identify novel and previously unsuspected genetic associations for those contributing to the excessive atherosclerosis, and those protective from atherosclerosis.